This invention relates generally to transducers and, more particularly, to audio transducer circuits particularly useful in intrusion alarm systems.
Intrusion alarm systems employ various type means, such as trip mechanisms, electromagnetic fields, and ultrasonic generators and receivers, for detecting entry into a given area and triggering some form of an alarm signal. In some systems, the first order alarm signal may comprise a flash of light or a pulse code on a radio signal, while in other systems, the first order alarm may comprise a sound wave, such as a siren, whistle, or a bang. For example, copending applications Ser. Nos. 803,563 and 803,565, filed June 6, 1977 and assigned to the present assignee, describe a flashlamp assembly for providing intense audible and visual signals when triggered by an act of intrusion. The assembly utilizes percussive flashlamps which operate in conjunction with associated pyrotechnic devices located in proximity to the transparent housing of the flashlamp assembly. Each pyrotechnic device provides an audible signal (a bang) in response to energy received from a respective flashlamp when the lamp is fired.
The audio transducer circuit of the present invention is particularly useful for providing one or more second order alarms of a more sustained or varied capability as an optional add-on feature for supplementing the aforementioned first order sound-producing devices. For example, see the above-listed copending application Ser. No. 940,062. Particular advantages of certain of the above-mentioned first-order alarm devices are low cost, simplified structure, and compactness. Accordingly, it is an object of the present invention to provide a low cost, compact audio transducer circuit compatible with the aforementioned sound-producing devices of the first order in an intrusion alarm system. The circuit could be adapted to battery operation if desired. Further, for applications such as the aforementioned flashlamp-actuated pyrotechnic elements, the transducer circuit should be operative to generate a sustained alarm in response to a sound pulse of comparatively short duration.